JP2004113779A - X-ray ct device and method for ct value measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the high x-ray scanning time for a subject to reduce the amount of exposure. <P>SOLUTION: Surrounding a subject who has been infused with a contrast medium, an x-ray tube and an x-ray detector are placed to collect his/her x-ray projection data, which are to be processed for reconstruction in order to create image data for both preliminary and main radiographic performances. A CT value calculation circuit, in the preliminary radiography carried out prior to the main radiography, sequentially calculates CT values in each region of interest (ROI), as a pre-set prescribed area, of a plurality of image data obtained one after another. The calculated CT values are displayed as a time-based time-density-curve (TDC), to show when and how the inflow and outflow of the contrast medium are made in the ROI. Based on the inflow and outflow timing, the starting and ending time of the main radiography can be optimally determined. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an X-ray CT apparatus, and more particularly, to an X-ray CT apparatus and a CT value measuring method capable of observing a CT value.

In recent X-ray CT apparatuses, real-time display of X-ray CT images has been realized by high-speed image reconstruction performed in parallel with X-ray data acquisition with the increase in speed and performance of X-ray detection apparatuses and arithmetic processing apparatuses. It has become possible.

ダ イ ナ ミ ッ ク Furthermore, a dynamic CT imaging method to which such a high-speed imaging technique is applied has been developed and has already been put to practical use in a clinical setting. In the dynamic CT imaging method, a predetermined slice position is imaged a plurality of times, and a temporal change of the image is observed in real time. In particular, in a contrast dynamic CT imaging method using a contrast agent, arithmetic processing is performed based on temporal change information of a CT value indicating an amount of a contrast agent flowing in a blood vessel, and a calculated parameter such as a blood flow rate is imaged. As a result, hemodynamics in the body have been observed.

Contrast agents used in contrast dynamic CT imaging include types that exude from capillaries in the head, such as Xenon-based contrast agents, and accumulate in tissues, and those that exude from capillaries, such as iodine-based contrast agents. There is no type, but recently the latter iodine-based contrast agents are used.

19A and 19B are diagrams showing a conventional contrast dynamic CT imaging method. FIG. 19A shows the timing of injection of a contrast agent, the start and end of imaging, and FIG. 19B shows the contrast agent in an imaging slice. Indicates the amount of

In contrast-enhanced dynamic CT imaging using an iodine-based contrast agent, imaging is started after a predetermined time T1 after injection of the contrast agent into the elbow vein, and is ended after a predetermined time T2. The time T1 corresponds to the time required for the contrast agent injected into the elbow vein to reach the slice to be imaged, and the time T2 corresponds to the time required for the contrast agent to flow into the slice plane and flow out (disappear). Equivalent.

Since these times depend on the speed of blood flow and therefore vary from subject to subject, T1 is the shortest value and T2 is the longest value, taking into account the range of variation between subjects. Are set empirically.

According to this method, a large margin is included in the period from the start of imaging to the end of imaging, and the subject may be exposed to a large amount of X-rays.

As a first method for solving such a problem, first, a low X-ray scan using a low dose is performed on a slice position requiring diagnosis, and a predetermined slice position obtained by this low X-ray scan is obtained. If the contrast agent is displayed on a blood vessel in the CT image, a method of switching to a high X-ray scan using a high dose can be considered.

On the other hand, as a second method, a preparation image is taken at the slice position, and the position of a region of interest (hereinafter, referred to as ROI) is set in a region of the obtained preparation image data, in particular, a region where a blood vessel is displayed. . Then, a low X-ray scan is performed on the slice position, and a CT value of the obtained image data at the position of the ROI is measured. When the CT value exceeds a preset threshold, a high X-ray scan is performed. There is a method to automatically switch to. (For example, refer to Patent Document 1).

As a third method, similarly to the above-described method, the timing at which the CT value of the image data obtained by the low X-ray scan at a predetermined ROI exceeds the first threshold value is automatically detected. A high X-ray scan is started based on this. Also, a method has been proposed in which the CT value in the ROI on the image obtained by the high X-ray scan automatically detects the timing at which the CT value falls below the second threshold value in the same manner, and terminates all CT imaging. (For example, see Patent Document 2).
JP-A No. 11-342125 (pages 3-6, FIGS. 1-4) JP-A-6-114049 (pages 2-4, FIG. 1-4)

In the above-described first method, it is possible to recognize that the contrast agent has arrived from a CT image at a predetermined slice position obtained by a low X-ray scan using a low dose. Since it cannot be predicted, it is difficult to accurately set the start timing of the high X-ray scan.

In the second method and the third method, the apparatus automatically sets the start timing or the end timing of the high X-ray scan by comparing the CT value of the blood vessel region with a preset threshold value. Although a method is employed, it is actually difficult to accurately determine the start timing and the end timing of the high X-ray scan from comparison with a uniquely set threshold value. This is because the peak value and shape of a CT-value change curve (time-density-curve: hereinafter, referred to as TDC) differ depending on the subject. Therefore, conventionally, it is difficult to accurately determine the irradiation timing (particularly the irradiation end timing) in the high X-ray scan, and the patient may receive a large amount of X-ray in the high X-ray scan.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an X-ray CT apparatus and a CT value capable of collecting necessary information without omission and reducing unnecessary X-ray exposure as much as possible. It is to provide a measuring method.

In order to solve the above problem, an X-ray CT apparatus according to the present invention according to claim 1 includes an X-ray irradiating unit configured to irradiate an X-ray to a subject, and an X-ray CT detecting an X-ray transmitted through the subject. X-ray detection means, image data generation means for generating image data based on projection data at a desired position of the subject collected using the X-ray irradiation means and the X-ray detection means, and the image data generation means Region-of-interest setting means for setting a region of interest for the first image data before the injection of the contrast agent obtained by the method described above, and a plurality of pieces of second image data after the injection of the contrast agent by the image data generating means. In parallel with the generation, a CT value measuring unit that measures a CT value in the region of interest set in the second image data based on the position information of the region of interest set by the region of interest setting unit; It is characterized in that it comprises a CT value display means for displaying the temporal change of the measured CT value by the value measuring means.

Further, the X-ray CT apparatus according to the present invention according to claim 5, X-ray irradiating means for irradiating the subject with X-rays, X-ray detecting means for detecting X-rays transmitted through the subject, Image data generating means for generating image data based on projection data at a desired position of the subject collected using X-ray irradiating means and the X-ray detecting means, and a contrast agent obtained by the image data generating means In parallel with the region of interest setting means for setting a region of interest for the first image data before injection, and the generation of a plurality of continuous second image data after injection of the contrast agent by the image data generating means, CT value measuring means for measuring a CT value in the region of interest set in the second image data based on the position information of the region of interest set by the region of interest setting means, and a threshold value related to the CT value is set. CT value comparing means for comparing the CT value obtained by the CT value measuring means with the threshold value set by the threshold value setting means over time, and outputting a coincidence signal when the two substantially match. And irradiation condition setting means for updating irradiation conditions for the subject based on the output signal of the CT value comparing means.

Further, the X-ray CT apparatus according to the present invention according to claim 17, X-ray irradiating means for irradiating the subject with X-rays, X-ray detecting means for detecting X-rays transmitted through the subject, A moving means for moving the subject in a predetermined direction, and a continuous means based on projection data of the subject collected by using the X-ray irradiating means and the X-ray detecting means while moving the subject by the moving means. Image data generating means for generating a plurality of pieces of image data, a region of interest setting means for setting a region of interest of a desired size to the image data generated by the image data generating means, In parallel with the generation, a CT value measuring unit for measuring a CT value of the image data in the region of interest is provided.

The X-ray CT apparatus according to the present invention according to claim 19, further comprising: an X-ray irradiating unit configured to irradiate X-rays in a plurality of directions of the subject; and an X-ray detection unit configured to detect X-rays transmitted through the subject. Means, moving means for moving the object in a predetermined direction, and projection data of the object collected using the X-ray irradiating means and the X-ray detecting means while moving the object by the moving means Image data generating means for generating a plurality of continuous image data based on the, and a region of interest setting means for setting a region of interest of a desired size for the image data generated by the image data generating means, In parallel with the generation of the image data, a CT value measuring unit that measures a CT value of the image data in the region of interest in pixel units, a range setting unit that sets a range of CT values, and the CT value measuring unit. A number-of-pixels calculating means for calculating the number of pixels in the region of interest whose CT value is included in the range set by the range setting means, a threshold setting means for setting a threshold of the number of pixels, The number of pixels obtained by the number calculating means and the threshold value of the number of pixels set by the threshold value setting means are compared with time, and the pixel which outputs an instruction signal for stopping X-ray irradiation when the two almost match each other It is characterized by having number comparison means.

On the other hand, the CT value measuring method of the present invention according to claim 21 uses an X-ray irradiating unit and an X-ray detecting unit to generate first image data before injection of a contrast agent at a desired position of a subject; Setting a region of interest for measuring a CT value in the first image data, and using the X-ray irradiating means and the X-ray detecting means, after a contrast agent is injected at a desired position of the subject. Measuring a CT value in a region of interest set in the second image data based on the position information of the region of interest in parallel with generation of a plurality of continuous second image data; The method is characterized by having a step of displaying a temporal change of the obtained CT value.

A CT value measuring method according to the present invention according to claim 22, further comprising the steps of: setting a region of interest of a desired size at a desired position of the image data; X-ray irradiating means while moving the subject in a predetermined direction; In parallel with the generation of a plurality of continuous second image data performed using the X-ray detection means, the CT value in the region of interest set in the second image data based on the position information of the region of interest And a step of terminating the X-ray irradiating means of the X-ray irradiating means based on the measured CT value.

According to the present invention, it is possible to easily determine the optimum start timing or end timing in CT imaging. Therefore, since image data required for diagnosis is collected without excess or deficiency, useless X-ray irradiation on the subject can be reduced.

(Example 1)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

In this embodiment, in order to determine the start timing and the end timing of the high X-ray scan in the contrast dynamic CT imaging, the CT value of the image data is converted into the first low X-ray scan (first scan) and the high X-ray scan. The measurement is performed by a scan (second scan) and a second low X-ray scan (third scan). Then, the CT value obtained at this time is displayed in time series in real time as TDC.

(Structure of the device)
FIG. 1 is a block diagram illustrating a schematic configuration of the entire X-ray CT apparatus according to the present embodiment. The X-ray CT apparatus includes a bed 1 on which a subject 30 is placed, and the subject 30 and the subject 30. A gantry rotating unit 2 having an opening for inserting a top plate to be described later and rotating around the subject 30, and a couch / gantry mechanism 3 for moving and rotating the couch 1 and the gantry rotating unit 2 And a mechanism control unit 4 for controlling the mechanism unit 3, an X-ray generator 5 for irradiating the subject 30 with X-rays, and an X-ray for collecting X-ray data transmitted through the subject 30. And a projection data collection unit 6.

The X-ray CT apparatus includes an image data generating unit 7 that reconstructs the X-ray projection data collected by the X-ray projection data collecting unit 6 to generate CT image data, and measures a CT value from the image data. And a display unit 9 for displaying a CT image and a time-series change of the CT value, an input unit 10 for inputting imaging conditions and the like, and overall control of all these units. A system control unit 11 is provided.

The couch 1 has a couchtop slidable in its longitudinal direction by driving the couch / cradle mechanism 3, and the subject 30 usually has a body axis direction substantially coincident with the longitudinal direction of the couchtop. It is placed so that it does. Further, the mechanism control unit 4 controls the movement of the couch 1 in the long axis direction of the couchtop or the rotation of the gantry rotation unit 2 according to a control signal from the system control unit 11.

On the other hand, the X-ray generation unit 5 includes an X-ray tube 13 that irradiates the subject 30 with X-rays, a high-voltage generator 12 that generates a high voltage applied between an anode and a cathode of the X-ray tube 13, , An X-ray diaphragm 14 for collimating X-rays emitted from the X-ray tube 13, and a slip ring 15 for supplying power to the X-ray tube 13 installed on the gantry rotating unit 2.

The X-ray tube 13 is a vacuum tube that generates X-rays, and accelerates electrons by a high voltage supplied from the high-voltage generator 12 to generate X-rays by colliding with a tungsten target. The X-ray diaphragm 14 is located between the X-ray tube 13 and the subject 30 and has a function of narrowing the X-ray beam emitted from the X-ray tube 13 to a predetermined image receiving size to obtain a clear image. Have.

The X-ray diaphragm 14 shapes the X-rays emitted from the X-ray tube 13 into cone beam (quadrangular pyramid) or fan beam X-rays based on the effective field of view (FOV).

The gantry rotating unit 2 includes an X-ray tube 13 of an X-ray generating unit 5 that is opposed to the subject 30 inserted into an opening thereof, an X-ray detector 16 of an X-ray projection data collecting unit 6, and a switch. A group 17, a data collection circuit (hereinafter, referred to as DAS) 18, a transmission unit of a non-contact data transmission circuit 19, and a slip ring 15 are provided.

The X-ray tube 13 and the X-ray detector 16 are provided on the gantry rotating unit 2 rotatable with respect to the gantry fixing unit, and are parallel to the body axis direction of the subject 30 by a drive control signal of the mechanism control unit 4. High-speed rotation of 1 rotation / second to 2 rotations / second is performed around the central rotation axis.

The X-ray projection data collection unit 6 includes an X-ray detector 16 that detects X-rays transmitted through the subject 30, a switch group 17 that bundles signals from the X-ray detector 16 into a predetermined number of channels, a DAS 18, And a data transmission circuit 19. The X-ray detector 16 has a plurality of X-ray detection elements including a scintillator and a photodiode.

Next, a method of arranging the X-ray detecting elements in the X-ray detector 16 will be described with reference to FIG. FIG. 2A is a development view of the X-ray detector 16. In the multi-slice type X-ray detector 16, for example, the slice direction (Z direction) which is the body axis direction of the subject 30 is, for example, 40 mm. Elements, and 24 X-ray detection elements 51 are arranged in a channel direction (X direction) orthogonal to the slice direction. However, the X-ray detection elements 51 arranged in the channel direction are actually mounted on the gantry rotating unit 2 along an arc centered on the focal point of the X-ray tube 13. Then, in the slice direction of the X-ray detector 16, 16 X-ray detection elements 51 for obtaining data of 0.5 mm slice thickness are arranged at the center thereof, and the X-ray detection elements 51 of these 16 elements are arranged. At both ends, 12 X-ray detection elements 51 for obtaining data of 1.0 mm slice thickness are arranged.

Returning to FIG. 1, the switch group 17 of the X-ray projection data collection unit 6 transmits a signal detected by the X-ray detector 16 to the DAS 18 and transmits a signal received from the X-ray detection element in the slice direction to a predetermined value. The data is bundled to the number of channels and supplied to the DAS 18.

The DAS 18 has a multi-channel receiving unit, which converts a current signal from the X-ray detector 16 into a voltage, and further converts the current signal into a digital signal by an A / D converter (not shown) to project projection data. Generate

(4) The data transmission circuit 19 sends the projection data output from the DAS 18 to a projection data storage circuit 20 of the image data generation unit 7, which will be described later, by optical communication means, and stores the same. This data transmission method can be changed to another method as long as signal transmission between the rotating body and the fixed body is possible. For example, the slip ring described above may be used. However, in the X-ray detector 16, two-dimensional projection data is detected during one rotation (about one second), and in order to realize transmission of such a huge amount of projection data, the DAS 18 and data transmission are performed. The circuit 19 is required to have a high-speed processing function.

Next, “data bundling” in the above-described X-ray projection data collection unit 6 will be described with reference to FIG. However, in FIG. 2B, for simplicity of description, a case where ten X-ray detection elements 51-1 to 51-10 are arranged in one slice in the channel direction in the slice direction will be described.

That is, in the X-ray detector 16 of FIG. 2B, for example, four X-ray detection elements 51-4 to 51-7 are arranged at 1 mm intervals at the center in the slice direction, and 3 Element X-ray detection elements 51-1 to 51-3 and 51-8 to 51-10 are arranged at 2 mm intervals, respectively. On the other hand, the DAS 18 includes, for example, four columns of receiving units 52-1 to 52-4, and the switch group 17 bundles, for example, ten columns of received signals detected by the X-ray detection element into four columns.

ス ラ イ ス By this “data bundling”, it becomes possible to change the slice thickness in the multi-slice. For example, by connecting the X-ray detection elements 51-4 to 51-7 to the receiving units 52-1 to 52-4 of the DAS 18 via the switch group 17, data of a slice width of 1 mm for four slices can be obtained. . On the other hand, when four pieces of data having a slice width of 2 mm are required, the X-ray detecting element 51-3 is used as the receiving unit 52-1, and the X-ray detecting elements 51-4 and 51-5 are used as the receiving unit 52-2. The line detecting elements 51-6 and 51-7 are connected to the receiving unit 52-3, and the X-ray detecting element 51-8 is connected to the receiving unit 52-4.

(4) Such “data bundling” makes it possible to cope with both a case where a narrow region is photographed with high resolution and a case where a wide region is photographed with high sensitivity.

Returning to FIG. 1 again, the image data generation unit 7 includes a projection data storage circuit 20, a reconstruction operation circuit 21, and an image data storage circuit 22.

The projection data storage circuit 20 is a storage circuit for storing the projection data of the subject 30 detected by the X-ray detector 16 and sent via the data transmission circuit 19. The image data storage circuit 22 is a storage circuit for storing image data generated by reconstructing the projection data. In the present embodiment, the preparation image data for setting the ROI for CT value measurement, the high X-ray scan image data for clinical diagnosis, the second X-ray scan for detecting the imaging start timing and the imaging end timing for this high X-ray scan The X-ray projection data collected to generate the first low X-ray scan image data and the second low X-ray scan image data is stored in the projection data storage circuit 20. Each image data obtained by reconstructing these projection data is stored in the image data storage circuit 22.

The reconstruction operation circuit 21 performs a reconstruction process on the projection data stored in the projection data storage circuit 20 to prepare a preparation image, a first low X-ray scan image, a high X-ray scan image, and a second Each image data of the low X-ray scan image is generated.

On the other hand, the CT value measurement unit 8 includes an ROI position storage circuit 24, a CT value calculation circuit 23, and a CT value storage circuit 25.

The ROI position storage circuit 24 stores the position information of the ROI set by the mouse of the input unit 10 described later in a predetermined position of the preparation image data. If it is determined in the first low X-ray scan or high X-ray scan that the setting of the ROI is not appropriate, the position information is changed according to the ROI change performed by the mouse operation or the keyboard operation of the operator. Be updated.

The CT value calculation circuit 23 generates the first low X-ray scan image data, the high X-ray scan image data, and the second low X-ray scan image based on the ROI position information stored in the ROI position storage circuit 24. The CT value of the data is measured, and the measurement result is stored in the CT value storage circuit 25.

The display unit 9 includes a display storage circuit 26, a conversion circuit 27, and a monitor 28. The display storage circuit 26 has an image data storage area for storing image data to be displayed on the monitor 28, and a TDC data storage area for storing data such as graphs such as TDC, numerical values such as CT values, or characters. . The latest image data is sequentially updated and stored in the image data storage area, and the first low X-ray scan, high X-ray scan, or second low X-ray scan is stored in the TDC data storage area. CT values obtained from the image data are stored. These monitor display data are displayed on the monitor 28 after D / A conversion and television format conversion are performed by the conversion circuit 27. The operator can interact with the device by using the monitor 28 and the input unit 10 of the display unit 9.

The input unit 10 is an interactive interface including input devices such as a display panel, a keyboard, various switches, and a mouse. An operator sets various imaging conditions via the input unit 10 before capturing a CT image. Perform Further, at the stage where the preparation image data is selected, the operator sets an ROI for CT value measurement on this image. Further, when it is determined that the ROI position is inappropriate during the first low X-ray scan or the high X-ray scan, the ROI can be changed or newly set in the same procedure.

The system control unit 11 includes a CPU and a storage circuit (not shown), and temporarily stores various photographing conditions and various command signals sent from the input unit 10 in an internal storage circuit. In accordance with an instruction from the input unit 10, each unit of the system such as the mechanism control unit 4, the X-ray generation unit 5, the X-ray projection data processing unit 6, the image data generation unit 7, the CT value measurement unit 8, and the display unit 9 is controlled. Control. In parallel with the execution of each scan, reconstruction processing and CT value measurement are performed using data obtained by these scans, and the results are displayed. By repeating such operations, real-time display of image data and TDC data is performed.

(Imaging procedure of contrast-enhanced dynamic CT image)
Next, an imaging procedure of a contrast-enhanced dynamic CT image according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a flowchart showing the photographing procedure in this embodiment.

(4) The operator of the apparatus inputs various imaging conditions from the input unit 10 prior to imaging of the X-ray CT image, whereby the system control unit 11 stores the imaging conditions in a storage circuit (not shown) (step S1). The imaging conditions set at this stage include X-ray projection data acquisition conditions, reconstruction conditions, image display / recording conditions, and the like.

The X-ray projection data acquisition conditions include an imaging region, a scanning method, a slice interval, the number of slices, a tube voltage / tube current, an imaging region size, a scan interval, a view interval, and a moving speed of the bed 1. In particular, the tube current and the scan interval are important parameters in reducing the X-ray dose in the present embodiment.

The X-ray projection data acquisition conditions for the low X-ray scan using the low X-ray dose and the high X-ray scan using the high X-ray dose are set, for example, to the values shown in FIG. That is, the tube current of the first low X-ray scan is 50 mA, the scan interval is 2 seconds, the tube current of the high X-ray scan is 100 mA, the scan interval is 1 second, and the tube current of the second low X-ray scan is 70 mA, the scan interval is 2 seconds. However, any one of the tube current and the scan interval shown in this figure may be selected and set. Note that the scan interval is an image capture interval of a plurality of image data captured at a predetermined slice position. For example, when the scan interval is 2 seconds, the rotation speed of the X-ray tube 13 and the X-ray detector 16 Is one rotation / second, one shot is performed every two rotations. On the other hand, the view interval is a data acquisition interval in the rotation direction of the X-ray tube 13 and the X-ray detector 16.

On the other hand, the reconstruction conditions include a reconstruction method, a reconstruction area size, a reconstruction matrix size, and the like, and the image display / recording conditions include a CT image display format and a TDC display format.

When the setting of the above conditions is completed, the subject 30 is placed on the top of the couch 1 and the top and the top are set so that the site to be observed of the subject 30 is at a predetermined position of the gantry opening. The subject 30 is moved in the body axis direction (Step S2). Next, the preparation image is photographed. The preparatory image data is image data that is imaged in advance to determine the position of the imaging slice with respect to the diagnostic region of the subject 30. In the present embodiment, the ROI for CT value measurement is used in this embodiment. Make settings. As the scanning method, the method set in step S1 is used. Here, a multi-slice method in which the slice thickness is 2 mm and the number of slices is 4 will be described.

In photographing the preparatory image data, the operator inputs an instruction signal for movement of the subject 30 and rotation of the gantry from the input unit 10, and the system control unit 11 transmits a command to the bed / The gantry mechanism 3 is controlled. That is, the couch / gantry mechanism unit 3 moves the subject 30 by a predetermined distance in the body axis direction, and then the X-ray tube 13 and the X-ray detector 16 are arranged so as to sandwich the subject 30 therebetween. The gantry rotating unit 2 is rotated at a speed of 1 rotation / second or more to collect X-ray projection data of the subject 30.

Hereinafter, an outline of the operation of the apparatus in the generation of X-ray CT image data will be described taking the preparation image data as an example, but a first low X-ray scan, a high X-ray scan, and a second low X-ray scan described later. Image data generation in scanning is performed in substantially the same procedure.

When irradiating the subject 30 with X-rays, the high-voltage generator 12 generates an X-ray for preparing image data capturing according to the setting conditions of the tube voltage and the tube current stored in a storage circuit (not shown) of the system control unit 11. The electric power (tube voltage and tube current) required for irradiation is supplied to the X-ray tube 13. The X-ray tube 13 irradiates the subject 30 with cone beam X-rays or fan beam X-rays by receiving the power supply. In capturing the preparatory image data, the X-ray tube 13 is supplied with power corresponding to the X-ray dose similar to the high X-ray scan, and the scan interval is set similarly to the high X-ray scan.

The X-rays emitted from the X-ray tube 13 are detected by the X-ray detector 16 of the X-ray projection data collection unit 6 after transmitting through the subject 30. That is, the X-rays transmitted through the subject 30 are converted into electric charges proportional to the transmitted dose by the X-ray detectors 16 arranged in the X-ray detector 16 in the slice direction and 912 elements in the channel direction. Amplification processing and A / D conversion are performed in four rows of receiving units 52 in the data acquisition circuit (DAS) 18 via the switch group 17 to form X-ray projection data.

Next, the X-ray projection data is sent to the data transmission circuit 19, and the transmission unit of the data transmission circuit 19 mounted on the gantry rotating unit 2 converts the electric signal into an optical signal. This optical signal is received by the receiving section of the data transmission circuit 19 of the gantry fixing section via the air, and these data are stored in the projection data storage circuit 20 of the image data generating section 7. That is, the X-ray tube 13 and the X-ray detector 16 repeat the above-described detection operation at a frequency of, for example, 1000 times per rotation while continuously rotating around the subject 30. Then, the projection data obtained at this time is stored in the projection data storage circuit 20 via the switch group 17, the DAS 18, and the data transmission circuit 19.

In this way, for example, if the X-ray projection data at the four slice positions set to the slice thickness of 2 mm is stored in the projection data storage circuit 20, the reconstruction operation circuit 21 executes the X-ray projection for the four slices. For each of the data, for example, the projection data obtained in the range of 180 ° + fan beam angle is read out and subjected to a reconstruction process to generate four image data. The obtained image data is stored in the image data storage circuit 22.

On the other hand, the CPU (not shown) of the system control unit 11 temporarily stores the image data of the four slices in the display storage circuit 26, performs D / A conversion and TV format conversion in the conversion circuit 27, and displays the data on the monitor 28. I do.

Next, while sequentially moving the subject 30 in the body axis direction at a preset slice interval (for example, 1 mm interval), the operator captures image data at different slice positions a plurality of times by the above procedure. Then, from the plurality of pieces of image data obtained in this manner, a slice position that is considered to be optimal for contrast dynamic CT imaging described later is selected (step S3).

Next, an ROI for CT value measurement is set for the preparation image data at the optimal slice position. The operator displays the prepared image data on the monitor 28 of the display unit 9 and sets a plurality of ROIs on the image using the mouse or keyboard of the input unit 10.

FIG. 5 is a diagram showing the setting of the ROI in the head preparation image. In this case, the operator sets a plurality of ROIs (ROI1 to ROI4) for the blood vessels (blood vessels 1 to 4) displayed in the preparation image and adds identification numbers (1 to 4). In particular, it is desirable to display the blood vessel 1 (artery) reaching the earliest contrast agent and the blood vessel 4 (vein) reaching the latest, which are important in the present embodiment, separately from other ROIs. Is arranged near the ROI as an INDEX with characters such as "early-sign" and "reference" for the latter. When the identification number or INDEX prevents image observation, the ROI may be identified by the shape, line type, or color of the boundary line, as shown in FIG. The shape of the ROI can be easily changed by dragging the ROI boundary line with a mouse. The ROI information (position information, size, boundary information, etc.) set by the mouse of the input unit 10 is stored in the ROI position storage circuit 24 via the system control unit 11 (step S4).

When the setting of the CT value measurement ROI in the preparation image data is completed, the operator injects an iodine-based contrast medium into the elbow vein of the subject 30 and, after a predetermined time T0, inputs the first low X-ray from the input unit 10. A scan start command signal is input (step S5). The command signal is sent to the system control unit 11, and an area for storing TDC data is newly set in the display storage circuit 26 in addition to an area for storing image data in accordance with the display conditions already stored in the system control unit 11. Is done.

On the other hand, the system control unit 11 having received the first low X-ray scan start command from the input unit 10 sends the projection data acquisition conditions for the first low X-ray scan to the X-ray projection data acquisition unit 6 and again. The configuration conditions are sent to the image data generation unit 7 to control them. On the other hand, the system control unit 11 sends a control signal to the high-voltage generator 12 to realize the first low-X-ray scan with a low X-ray dose, and the high-voltage generator 12 And a tube voltage and a tube current corresponding to the low X-ray irradiation.

X-rays emitted from the X-ray tube 13 are transmitted through the subject 30 and then detected by the X-ray projection data collection unit 6 to form projection data at four slice positions. The projection data at the optimum slice position selected from the projection data at the four slice positions is transferred from the transmission unit of the data transmission circuit 19 in the gantry rotation unit 2 to the reception unit of the data transmission circuit 19 in the gantry fixing unit. Then, the image data is stored in the projection data storage circuit 20 of the image data generator 7. The X-ray tube 13 and the X-ray detector 16 are rotated with respect to the subject 30 to perform the above-described detection operations from a plurality of directions. Projection data obtained at this time is transmitted through the switch group 17, the DAS 18, and the data transmission circuit 19. And stored in the projection data storage circuit 20.

When the X-ray projection data for one image is stored in the projection data storage circuit 20, the reconstruction operation circuit 21 reads out the X-ray projection data, performs a reconstruction process, and converts the obtained image data into image data. The data is stored in the storage circuit 22. On the other hand, the CPU (not shown) of the system control unit 11 temporarily stores the image data in the display storage circuit 26, performs D / A conversion and TV format conversion in the conversion circuit 27, and displays the data on the monitor 28.

Next, the CPU of the CT value calculation circuit 23 reads the image data stored in the image data storage circuit 22. Then, an ROI is set in the image data based on the position information of a plurality of ROIs already stored in the ROI position storage circuit 24, and a CT value in each ROI is measured. However, when the ROI is composed of a plurality of image pixels, the maximum value is extracted from a plurality of CT values obtained from each pixel and stored in the CT value storage circuit 25 as a representative CT value. Alternatively, an average value may be used as the representative CT value instead of the maximum value.

By the way, the CT value represents the X-ray absorption coefficient of the substance to be measured as a relative value to the basic substance, and is represented by CT value = K [(μ−μ0) / μ0]. Here, μ is the X-ray absorption coefficient of the substance to be measured, μ0 is the X-ray absorption coefficient of the basic substance, and K is a constant. In general, K = K so that the CT value of water is 0 and the CT value of air is −1000. It is 1000. The X-ray absorption coefficient indicates the ratio of X-ray absorption per unit thickness.

The display storage circuit 26 receives a control signal relating to display conditions from the system control unit 11, and replaces the preparatory image data already stored in the image data storage area with the first low X-ray scan obtained. Save the image data. At this time, the supplementary information on the position and shape of the ROI displayed in the preparation image data is stored in the same image data storage area as it is. Further, the CT value of the first image data obtained by the first low X-ray scan is stored in the TDC data storage area of the same display recording circuit 26.

In this manner, in the image data storage area of the display storage circuit 26, the first image data obtained by the first low X-ray scan and a plurality of ROI boundaries are stored. In the TDC data storage area, the CT value of the first image data obtained by the first low X-ray scan is stored for each ROI. These data are displayed on the monitor 28 in real time via the conversion circuit 27 (step S6).

When the gantry is rotated at a constant speed, a predetermined time (scan interval: Δt1) after the first image data is obtained by the first low X-ray scan, the system control unit 11 Then, the high voltage generator 12 supplies the X-ray tube 13 with a tube voltage and a tube current corresponding to the low X-ray dose. The X-ray tube 13 to which power required for X-ray irradiation has been supplied irradiates the subject 30 with X-rays, and the X-ray projection data collection unit 6 collects projection data of the subject 30 at the optimal slice position. . Similarly, while the gantry rotating unit 2 makes one rotation at high speed, the X-ray projection data collecting unit 6 collects projection data on the subject 30 from a plurality of directions. Further, the image data generation unit 7 generates second image data by the first low X-ray scan using these projection data, and stores the second image data in the image data storage circuit 22.

On the other hand, the CPU of the CT value calculation circuit 23 reads out the second image data by the first low X-ray scan stored in the image data storage circuit 22. Next, based on the position information of the plurality of ROIs already stored in the ROI position storage circuit 24, an ROI is set for the second image data by the first low X-ray scan. Then, the CT value in each of these ROIs is obtained, and the result is stored in the CT value storage circuit 25 for each ROI.

Next, the system control unit 11 replaces the first image data of the first low X-ray scan already stored in the display storage circuit 26 with the newly obtained second image data of the first low X-ray scan. And a plurality of the ROI boundaries described above are added to the image data. Further, the CT value in the second image data of the first low X-ray scan measured by the CT value calculation circuit 23 is also sent to the TDC data storage area of the display storage circuit 26 and has already been stored. It is stored adjacent to the CT value in the first image data of the first low X-ray scan.

Therefore, on the monitor 28, the second image data of the first low X-ray scan to which a plurality of ROIs are added and the CT values measured in the first and second image data of the first low X-ray scan Are displayed in chronological order by ROI.

In the same manner, the generation of the third and subsequent image data by the first low X-ray scan and the measurement and display of the CT value at the optimum slice position are continuously performed at the scan interval Δt1. The obtained image data is sequentially stored in the image data storage circuit 22, and the latest image data is displayed on the monitor 28 with the ROI added.

The CT value calculation circuit 23 measures the CT value in the first low X-ray scan image data stored in the image data storage circuit 22 based on ROI position information set in advance. I do. Further, the measured CT value is stored in the CT value storage circuit 25, and the value is displayed in time series on the TDC of the monitor 28. In this case, information such as the identification number of the corresponding ROI and INDEX is added to each TDC.

FIG. 6 shows the TDC at the end of the first low X-ray scan, and the monitor 28 displays a CT image 110a of the head in the first low X-ray scan and a TDC graph 110b of the CT value. Is displayed. However, in the TDC graph 110b, a solid line indicates a TDC obtained by a first low X-ray scan, and a broken line indicates a TDC obtained by a high X-ray scan and a second low X-ray scan described later. .

In the initial first low X-ray scan, a plurality of pieces of image data are often collected without the contrast agent reaching the ROI. In such a case, it is desirable to add and average the values of the respective pixels in the plurality of pieces of image data and store and display the data as one piece of image data. According to this method, the number of images can be reduced, and image data having a high S / N can be obtained.

Next, the operator observes the TDC of each ROI displayed on the monitor 28, and estimates the timing at which the contrast agent arrives from the change curve. For example, attention is particularly paid to the TDC (α1 in the TDC graph 110b) in the ROI tagged as “early-sign” because the contrast agent reaches the earliest in the slice plane of the CT image. Then, the timing of the start of the high X-ray scan is determined by comprehensively judging from the latest value or information such as the shape (gradient) of the curve (step S7).

(4) If the operator determines from the TDC information that it is the optimum timing for starting the high X-ray scan, the operator inputs a high X-ray scan start command signal from the input unit 10 (step S8). The system control unit 11 receives this command signal and sends a control signal for high X-ray scanning to the high voltage generator 12, and the high voltage generator 12 sends a control signal for high X-ray scanning to the X-ray tube 13. The tube voltage and the tube current are increased and supplied in order to perform the X-ray irradiation.

In this high X-ray scan, the slice thickness of the multi-slice may be reduced (for example, 1 mm) in order to improve the resolution in the slice direction. At this time, the deterioration of the X-ray detection sensitivity due to the narrowing of the width of the X-ray detection element 51 may be compensated for by increasing the tube current.

The X-ray tube 13 receives supply of X-ray irradiation power from the high voltage generator 12 and converts X-rays to be irradiated on the subject 30 from a low X-ray dose for the first low X-ray scan to a high X-ray scan. Change to high X dose. Then, the X-ray projection data acquisition unit 6 acquires X-ray projection data for four slices in the same manner as in the case of the first low X-ray scan. That is, the X-ray projection data collection unit 6 collects X-ray projection data obtained from a plurality of directions while rotating the gantry at high speed for four slices, and the image data generation unit 7 uses these projection data. First image data by the high X-ray scan is generated and stored in the image data storage circuit 22 (step S9).

The CT value calculation circuit 23 selects the image data at the optimum slice position from the first image data of the high X-ray scan stored in the image data storage circuit 22. Next, based on the position information of the plurality of ROIs already stored in the ROI position storage circuit 24, the CT value in the ROI set in the selected image data is obtained, and stored in the CT value storage circuit 25 for each ROI ( Step S10).

In the image data storage area of the display storage circuit 26, the system control unit 11 starts with the last image data of the first low X-ray scan and the first image data of the high X-ray scan at the optimal slice position already stored. And the previously set ROI information is added to this high X-ray scan image data as it is and stored.

Further, the system control unit 11 supplies the CT value in each ROI of the first image data of the high X-ray scan measured by the CT value calculation circuit 23 to the TDC data storage area of the display storage circuit 26, Is stored adjacent to the CT value obtained in the last image data of the low X-ray scan. Accordingly, the first image data of the high X-ray scan once stored in the display storage circuit 26 is displayed on the monitor 28 of the display unit 9, and further, a plurality of CT values in the first low X-ray scan image data are displayed. Then, the TDC of the CT value in the high X-ray scan image data is displayed for each ROI (step S11).

After the first image data of the high X-ray scan is obtained and after the scan interval Δt2, the second image data of the high X-ray scan is collected by the same procedure as that of the first image data of the high X-ray scan, and the image is acquired. The data is stored in the data storage circuit 22. Note that the scan interval Δt2 for image data acquisition in the high X-ray scan and the scan interval Δt1 for image data acquisition in the first low X-ray scan are, as described above, imaging conditions set by the operator before the start of imaging. And it is preferable to set Δt1> Δt2.

That is, in the high X-ray scan as compared to the first low X-ray scan, the image data acquisition interval is shortened to improve the time resolution of the image. On the other hand, the first low X-ray scan aims to know the optimal start timing of the high X-ray scan in order to shorten the time required for the high X-ray scan with a large exposure dose as much as possible. . Therefore, in the first low X-ray scan that does not require high image sensitivity and time resolution, the dose in one X-ray irradiation is reduced, and the scanning interval is lengthened to reduce the number of irradiations per unit time. (1) The exposure dose in one contrast dynamic CT imaging can be reduced.

Next, the system control unit 11 updates the first image data of the high X-ray scan stored in the display storage circuit 26 to the second image data of the high X-ray scan. On the other hand, the CPU of the CT value calculation circuit 23 measures the CT value in each ROI of the second image data of the high X-ray scan stored in the image data storage circuit 22, and further, the CPU calculates the obtained CT value. The value is stored in the CT value storage circuit 25. Next, the system control unit 11 sends the CT value to the TDC data storage area of the display storage circuit 26, and stores the first low X-ray scan and the first image data of the high X-ray scan already stored. Store with CT value. Then, the second image data of the high X-ray scan and the TDC data of the CT value stored in the display storage circuit 26 are displayed on the monitor 28 via the conversion circuit 27.

In the same manner, the generation of the third and subsequent image data by the high X-ray scan and the measurement and display of the CT value at the optimum slice position are continuously performed at the scan interval Δt2. Then, on the monitor 28, as shown in FIG. 7 described later, the latest high X-ray scan image to which a plurality of ROIs are added and the TDC of CT values obtained by the first low X-ray scan and the high X-ray scan The data is displayed.

By the way, the position of the ROI set in the preparation image data before the administration of the contrast agent may not always be optimal. That is, the operator observes the first low X-ray scan image or high X-ray scan image displayed on the monitor 28. If it is determined that the previously set ROI position is not appropriate, the first low X-ray scan image or the high X-ray scan image displayed in real time is displayed in the same procedure as the ROI setting performed in the preparation image data. In the image, the position of the ROI is changed or a new ROI is set.

That is, the operator changes the ROI or newly sets the ROI for the first low X-ray scan image or the high X-ray scan image displayed on the monitor 28 using the mouse or keyboard provided in the input unit 10. Do. For example, when changing the position and size of the ROI using the keyboard, move the ROI with the arrow keys or the Page-Up / Page-Down key while selecting the ROI with the key of the same number as the identification number of the ROI. Is performed. At this time, the system control unit 11 sends the ROI information (position information, size, boundary line information, etc.) sent from the mouse of the input unit 10 to the ROI position storage circuit 24 and stores it.

On the other hand, the CPU of the CT value calculation circuit 23 outputs image data of the first low X-ray scan after the first image data of the first low X-ray scan stored in the image data storage circuit 22, Scan image data is sequentially read. Next, an ROI is set in the image data based on the position information of the changed ROI or the newly set ROI, and the CT value of each ROI is measured and stored in the CT value storage circuit 25.

On the other hand, the system control unit 11 stores the image data of the first low X-ray scan or the image data of the high X-ray scan in the image data storage area of the display storage circuit 26, and stores the image data in the ROI that has already been set. The CT value in the updated ROI or the new ROI is read out from the CT value storage circuit 25 and stored in the TDC data storage area together with the CT value. Therefore, the TDC from the first image data of the first low X-ray scan to the latest image data for the changed ROI or the new ROI is displayed on the monitor 28 for each ROI. In this case, it is desirable that the changed ROI, the new ROI, and the TDCs are distinguished from those of another ROI and displayed.

As described above, high-resolution contrast dynamic CT image data is generated by high X-ray scanning. The radiography by the high X-ray scan is continuously performed until the contrast agent injected into the subject 30 is discharged by the blood circulation in the body. It is important for.

The method of determining the end timing of the high X-ray scan in this embodiment is ultimately performed by the operator, similarly to the timing determination of the start of the high X-ray scan, but the X-ray CT apparatus determines the timing. It has a function of providing useful information to the operator.

That is, the operator observes a plurality of TDCs in each ROI displayed on the monitor 28 during the high X-ray scan imaging, and estimates the timing at which most of the contrast agent is discharged from the change curve. In particular, paying attention to the TDC in the ROI tagged as “reference” as the contrast agent disappears at the latest in the slice plane of the CT image, and comprehensively judge from the latest value or the shape of the curve. The timing is determined (step S12).

FIG. 7 shows the TDC at the end of the high X-ray scan, and the monitor 28 displays a CT image 111a of the head in the high X-ray scan and a TDC graph 111b of the CT value. However, in the TDC of the TDC graph 111b, the solid line portion is the TDC obtained by the first low X-ray scan and the high X-ray scan, and the broken line portion is the TDC by the second low X-ray scan described later.

In the TDC displayed on the monitor 28, for example, the TDC (α2 in the TDC graph 11b) in the ROI tagged with “reference” as the contrast agent arrives at the latest in the slice plane of the CT image Pay special attention. Then, when the end timing of the main imaging is determined from the latest value or the shape such as the slope of the curve, a second low X-ray scan start command is input from the input unit 10 (step S13).

The system control unit 11 receives the input command signal and sends a second low X-ray scan control signal to the high voltage generator 12, and the high voltage generator 12 sends the second low X-ray scan signal to the X-ray tube 13. A tube voltage and a tube current for performing low X-ray irradiation similar to the case of the low X-ray scan of No. 1 are supplied. The X-ray tube 13 irradiates the subject 30 with X-rays changed from the high X-ray dose for high X-ray scan to the low X-ray dose for the second low X-ray scan, and the X-ray projection data collection unit 6 X-ray projection data at the optimal slice position of the subject 30 is collected from a plurality of directions while rotating the gantry at high speed. On the other hand, the image data generation unit 7 generates image data of the second low X-ray scan using these projection data, and stores the image data in the image data storage circuit 22.

The CT value calculation circuit 23 reads the first image data of the second low X-ray scan stored in the image data storage circuit 22. Then, the CT value of the image data is obtained based on the plurality of ROI position information stored in the ROI position storage circuit 24, and is stored in the CT value storage circuit 25 for each ROI.

On the other hand, the system control unit 11 updates the last stored high X-ray scan image data to the first image data of the second low X-ray scan in the image data storage area of the display storage circuit 26, The already set ROI information is added to this second low X-ray scan image data as it is and stored.

Further, the system control unit 11 supplies the CT value in each ROI of the first image data of the second low X-ray scan measured by the CT value calculation circuit 23 to the TDC data storage area of the display storage circuit 26. Then, it is stored adjacent to the CT value obtained in the last high X-ray scan image data. Therefore, the first image data of the second low X-ray scan once stored in the display storage circuit 26 is displayed on the monitor 28 of the display unit 9. Further, CT values obtained from the first image data of the second low X-ray scan together with CT values in the first low X-ray scan image data and the high X-ray scan image data are displayed in time series as TDC. (Step S14).

Next, after obtaining the first image data of the second low X-ray scan, the second image data of the second low X-ray scan is collected after a scanning interval Δt3. Then, the second image data of the second low X-ray scan and the CT value obtained from this image data are stored in the image data storage circuit 22 and the CT value storage circuit 25 in the same procedure as described above, and 28 is displayed. Note that the scan interval Δt3 in the generation of the second low X-ray scan image data is larger than the scan interval Δt2 of the high X-ray scan and is set to a value substantially equal to the scan interval Δt1 of the first low X-ray scan. .

In the same manner, generation of the third and subsequent image data by the second low X-ray scan and measurement and display of the CT value at the optimum slice position are continuously performed at the scan interval Δt3. The obtained image data is sequentially stored in the image data storage circuit 22, and the latest image data is displayed on the monitor 28 with the ROI added.

The CT value calculation circuit 23 measures the CT value in the ROI of the third low X-ray scan image data stored in the image data storage circuit 22 based on the preset ROI position information. I do. Further, the measured CT value is stored in the CT value storage circuit 25, and the TDC on the monitor 28 displays the value in time series.

The operator observes the TDC of the CT value obtained in the second low X-ray scan image data, and when confirming that the CT value has become equal to or less than a predetermined value, inputs an imaging end command from the input unit 10. (Step S15).

The system controller 11 supplies a control signal to the high voltage generator 12 based on the command signal for terminating the imaging to stop supplying the tube current and the tube voltage to the X-ray tube 13. Further, the system control unit 11 sends a stop signal to the mechanism control unit 4, stops all mechanism operations such as rotation of the gantry, and terminates imaging dynamic CT image data.

According to the first embodiment described above, the operator can easily determine the optimum start timing of the high X-ray scan from the CT value and the TDC shape obtained from the first low X-ray scan image data. And can be set accurately. Similarly, the optimal end timing of the high X-ray scan can be determined from the CT value obtained from the high X-ray scan image data and its TDC. Therefore, since image data required for high X-ray scanning can be collected without excess or deficiency, useless X-ray irradiation on the subject can be reduced.

In the above description, the process is shifted to the second low X-ray scan at the end of the high X-ray scan in order to make it easy to grasp the characteristics of the TDC of the CT value. By continuously measuring and displaying the CT value in the second low X-ray scan image data, it is easier to confirm the validity of the high X-ray scan end timing. Further, in order to further reduce X-ray irradiation on the subject 30, it is possible to end the contrast dynamic CT imaging at the end of the high X-ray scan.

(Example 2)
Next, a second embodiment of the present invention will be described with reference to FIGS.

In the second embodiment, to determine the start and end timings of the high X-ray scan in the contrast enhanced dynamic CT, the CT value of the image data is changed to the first low X-ray scan, the high X-ray scan, and the second low X-ray scan. Measured by X-ray scan. Then, in the TDC displaying these CT values in time series, it is displayed that this CT value has reached a preset threshold value.

In the first embodiment already described, the operator observes the TDC of the CT value measured in the ROI set in the first low X-ray scan image data and the high X-ray scan image data, and determines the shape of this curve. Alternatively, the start timing or the end timing of the high X-ray scan is determined from the latest CT value or the like.

On the other hand, in the present embodiment, before the first low X-ray scan is started, the CT value, the change rate of the CT value, the slope of the curve representing the shape of the change curve (TDC), or the slope of the curve A threshold value is set for the temporal change amount of. Then, if the TDC reaches the above threshold value during the CT value measurement, an arrival signal notifying the operator of that is generated. The operator determines the start timing and the end timing of the high X-ray scan with reference to the TDC of the CT value displayed on the monitor 28 and the arrival signal.

FIG. 8 shows a flowchart of the imaging procedure of contrast dynamic CT in this embodiment. However, in this flowchart, the same steps as those in the above-described first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

(4) The operator sets the imaging conditions (step S1), and then sets the position of the subject 30 (step S2). Furthermore, a plurality of pieces of CT image data of different slice planes are photographed for the subject 30, and image data at a slice position that is optimal for contrast dynamic CT photographing is selected from the plurality of pieces of CT image data as preparatory image data. (Step S3). Then, an ROI for CT value measurement is set at a desired position of the selected preparation image data (step S4).

Next, after completing the ROI setting on the preparation image, the operator inputs a threshold setting command from the input unit 10. The system control unit 11 receives this command signal and displays the ROI information stored in the ROI position storage circuit 24 on the monitor 28 in the form of a list. The operator selects a threshold input field set for each ROI in this list using the mouse of the input unit 10, further inputs a predetermined threshold from the keyboard, and ends the threshold setting. (Step S25).

Although each threshold may be set for each ROI, for example, high X-rays are set centering on the ROI set for the blood vessel (artery) reaching the contrast agent first and the blood vessel (vein) reaching the slowest. A scan start threshold and a scan end threshold may be set.

When the setting of the ROI for CT value measurement and the threshold in the preparation image is completed, the operator injects an iodine-based contrast medium into the elbow vein of the subject 30 and performs the first low X-ray scan after a predetermined time T0. Start (step S26).

The system control unit 11 performs the constant-speed rotation of the gantry rotation unit 2 and the constant-speed movement of the bed 1, and sets each of the image data obtained by the low X-ray scan at the scan interval Δt1 in the preparation image data. ROI is set based on the obtained ROI position information. Next, the CT value in this ROI is measured, and the obtained temporal change of the CT value is displayed on the display unit 9 as TDC (step S27).

When the CT value or the gradient of the TDC exceeds a predetermined threshold value during the measurement of the CT value in the first low X-ray scan image data, the system control unit 11 may perform, for example, a process shown in FIG. Thus, marking is performed at a predetermined position of the TDC (step S28). The operator estimates the timing at which the contrast agent arrives by referring to the above-described marking in addition to the CT value displayed on the monitor 28 and the shape of the TDC (step S29).

Next, when the operator detects the optimum timing of the start of the high X-ray scan from the information of the TDC, the operator inputs a command signal of the start of the high X-ray scan from the input unit 10 to start the high X-ray scan (step S30). ).

In the above description, the method of displaying the TDC when the operator determines the start timing of the high X-ray scan has been described. However, the timing of the end of the high X-ray scan can be determined by a similar procedure. That is, when the CT value or the gradient of the TDC reaches a predetermined threshold value during the measurement of the CT value in the high X-ray scan image data, marking is performed at a predetermined position of the TDC or the display unit 9 or the input unit. At 10, a predetermined signal is displayed.

The operator determines the timing at which the contrast agent disappears, that is, the timing at which the high X-ray scan ends, with reference to the marking in addition to the CT value displayed on the monitor 28 and the shape of the TDC. The high X-ray scan is terminated by inputting a command signal for ending the high X-ray scan or starting the second low X-ray scan from the input unit 10.

According to the second embodiment, in addition to the display of the TDC, which is a feature of the first embodiment, comparison information with respect to a preset threshold is obtained, so that the optimum start timing of the high X-ray scan by the operator is obtained. , And the end timing can be easily determined.

Although the first and second embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be modified and implemented. For example, another display method in the above embodiment is shown in FIGS. FIG. 10 shows a display example of image data. When many ROIs for CT value measurement are set on an image, the number of boundaries and various tags increases, and it becomes difficult to observe details in the image. . In such a case, the above problem is solved by displaying the diagnostic image 112a and the ROI setting image 112b separately.

FIG. 11 shows a TDC display method when a large number of CT value measurement ROIs are set. When a large number of ROIs are set, the number of TDCs also increases. In particular, it becomes difficult to observe TDCs in ROI1 and ROI4 which are important for judging the start and end timings of the high X-ray scan. Is separately displayed as the TDC graph 113b. At this time, the TDC shown in the TDC graph 113b may be deleted from the TDC graph 113a.

The shape of the ROI set on the CT image is not limited to a shape having an area such as a circle, an ellipse, and a rectangle, and may be a point-like ROI. However, in the case of a point ROI, it is desirable to average the CT values of surrounding pixels in order to prevent a reduction in S / N.

By the way, in contrast dynamic CT, the CT value increase may be more important than the CT value itself. In such a case, it is desirable to calculate and display the increase in CT value as TDC. In this case, the CT value of each ROI in the preliminary image or the initial image of the first low X-ray scan is used as the reference CT value.

In the above embodiment, an iodine-based contrast agent was used as a contrast agent, but the present invention is not limited to this, and a contrast agent such as a Xenon-based contrast agent may be used.

(Example 3)
Next, a third embodiment of the present invention will be described with reference to FIGS. In the above-described first embodiment, a second low X-ray scan is performed following the high X-ray scan in order to confirm the validity of the high X-ray scan end timing. The optimal end timing of the high X-ray scan was determined from the CT value obtained from the image data and the shape of the TDC.

However, it is also possible to automatically set the switching timing from the high X-ray scan to the second low X-ray scan and the end timing of the second low X-ray scan. In this case, for example, a predetermined ratio value (for example, 50%) is set as a threshold with respect to the maximum value of the CT value measured during the high X-ray scan, and the CT value continuously measured is compared with the threshold. By doing so, the variation in the switching timing between subjects is reduced.

FIG. 12 is a block diagram showing a schematic configuration of the X-ray CT apparatus according to the present embodiment. The difference from the first embodiment shown in FIG. It has been added to.

The CT value comparison circuit 29 detects the maximum value (maximum CT value) from the CT values in the high X-ray scan stored in the CT value storage circuit 25, and sets a threshold based on the maximum CT value. Further, the set threshold value is compared with the CT value calculated by the CT value calculation circuit 23 during the high X-ray scan. Then, when the CT value becomes equal to or less than the threshold value, a control signal for switching from the high X-ray scan to the second low X-ray scan is output.

Next, a procedure of imaging a contrast-enhanced dynamic CT image according to the third embodiment of the present invention will be described with reference to the flowchart of FIG. 13. However, in this flowchart, a procedure similar to that of the first embodiment shown in FIG. Are denoted by the same reference numerals, and a detailed description thereof will be omitted.

(4) The operator sets the imaging conditions (step S1), and then sets the position of the subject 30 (step S2). Further, the operator captures a plurality of pieces of CT image data on different slice planes of the subject 30 and prepares the optimal slice plane image data for contrast dynamic CT imaging from the plurality of pieces of CT image data in the preparation image. It is selected as data (step S3). Then, an ROI for CT value measurement is set at a desired position of the selected preparation image data (step S4).

When the setting of the ROI in the preparation image data is completed, the operator injects the contrast agent into the subject 30 and starts the first low X-ray scan (Step S5).

The system control unit 11 rotates the gantry rotation unit 2 at a constant speed, and based on the ROI position information already set in the preparation image data for each of the CT image data sequentially obtained by the low X-ray scan at the scan interval Δt1. To set the ROI. Next, the CT value in this ROI is measured, and the obtained temporal change of the CT value is displayed on the display unit 9 as TDC (step S6).

Next, the operator observes the TDC displayed on the display unit 8, estimates the timing at which the contrast agent arrives from the change curve, and determines the start timing of the high X-ray scan (Step S7).

Next, in accordance with the high X-ray scan start command signal input by the operator (step S8), the high voltage generator 12 supplies the X-ray tube 13 with a tube voltage and a tube current for high X-ray scan. .

The X-ray tube 13 receives supply of X-ray irradiation power from the high voltage generator 12 and converts X-rays to be irradiated on the subject 30 from a low X-ray dose for the first low X-ray scan to a high X-ray scan. Change to high X dose. The X-ray projection data collection unit 6 collects X-ray projection data in the same manner as in the case of the first low X-ray scan, and the image data generation unit 7 uses these projection data to generate high X-ray projection data. First image data by scanning is generated and stored in the image data storage circuit 22 (step S9).

On the other hand, the CT value calculation circuit 23 reads the first image data of the high X-ray scan stored in the image data storage circuit 22. Then, the CT value of the set ROI is measured based on the position information of a plurality of ROIs already stored in the ROI position storage circuit 24, and the result is stored in the CT value storage circuit 25 (step S10).

Similarly, the CT values of the second and subsequent image data of the high X-ray scan taken at the scan interval Δt2 are measured and stored in the CT value storage circuit 25. Then, the CT values obtained by the first low X-ray scan and the high X-ray scan are displayed on the monitor 28 as TDC.

On the other hand, the CT value comparison circuit 29 of the CT value measurement unit 8 reads a series of CT values measured by the CT value calculation circuit 23 according to the above procedure, and detects the maximum CT value obtained during the high X-ray scan. (Step S31). Then, a threshold is set based on the maximum CT value. As this threshold, for example, a value of 50% to 60% of the maximum CT value is set (step S32).

Next, the CT value comparison circuit 29 compares the set threshold value with the CT value in the latest image data sequentially supplied from the CT value calculation circuit, and when the CT value falls below the threshold value, An instruction signal for switching from the X-ray scan to the second low X-ray scan is supplied to the system control unit 11 (step S33).

(4) The system control unit 11, which has received the instruction signal, supplies a control signal to each unit to start a second low X-ray scan (step S13). Then, the CT value of the image data obtained by the second low X-ray scan in the ROI is measured and the TDC is displayed (step S14).

On the other hand, the operator observes the displayed TDC and confirms that the value has become equal to or less than the predetermined value, and inputs an imaging end command from the input unit 10 to end the imaging of the contrast enhanced dynamic CT image ( Step S15).

According to the third embodiment described above, when switching from the high X-ray scan to the second low X-ray scan, the switching timing is determined by comparing a preset threshold value and a CT value obtained by the high X-ray scan. Is automatically set, so that the burden on the operator is reduced.

The end timing of the second low X-ray scan may be automatically set by a procedure similar to the above-described switching from the high X-ray scan to the second low X-ray scan. In this case, the operator sets a threshold value β3 for determining the end timing of the second low X-ray scan in advance similarly to the threshold value β1 and the threshold value β2, and sets the CT value in the second low X-ray scan. When the value becomes equal to or smaller than the threshold value β3, the photographing ends. However, when it is difficult to set the threshold value β3 due to an increase in the baseline of TDC due to internal circulation of the contrast agent injected into the subject 30, the time of the maximum CT value obtained by the high X-ray scan ( TX1) and a time difference (ΔTX) between the switching time (TX2) from the high X-ray scan to the second low X-ray scan, and the second low X-ray scan is performed when a time ΔTX has elapsed from the TX2. It may end.

In the case where the switching timing is automatically set, the display of the CT value or TDC may not be performed. However, when the CT value becomes equal to or less than a preset threshold value, it is desirable to display the timing on the display unit 9 or the input unit 10. In this case, the scan switching instruction signal may be issued by the operator who observes the display on the display unit 9 or the input unit 10.

On the other hand, the above-described threshold has been described based on the case where the threshold is set based on the maximum CT value. However, the threshold may be a preset value or a value set from the input unit 10 by an operator or the like. May be performed at the time of setting the photographing conditions in step S2.

(Example 4)
Next, a fourth embodiment of the present invention will be described with reference to FIGS. 12, 14, and 15. FIG. This embodiment is an application of the first to third embodiments, and generates image data while moving the slice position at regular intervals. Then, by sequentially measuring the CT values in the image data, information as to whether or not the slice position is within the subject area is provided to the operator.

Note that collection of projection data, generation of image data, and a method of setting an ROI in the present embodiment are almost the same as those in the first embodiment, and thus detailed description is omitted.

FIG. 14 is a flowchart showing the photographing procedure of this embodiment. The operator sets various conditions for imaging and a threshold γ1 or γ2 for the CT value from the input unit 10 as in the first embodiment. (Step S51). However, the threshold γ1 is a threshold for detecting a boundary between a brain having a CT value of about 20 and a skull having a CT value of about 1000, and the threshold γ2 is a threshold for detecting a boundary between the skull and a CT of less than −2000. This is a threshold for detecting a boundary of air having a value. Hereinafter, a case where the threshold value γ1 is used will be described.

The operator places the subject 30 on the top of the bed 1 (step S52), and moves the top and the subject so that the diagnosis site (for example, the head) of the subject 30 is at a predetermined position in the gantry opening. 30 is moved in the body axis direction. Then, the first image data is photographed as preparatory image data (step S53), and one or a plurality of ROIs are set for this image data (step S54).

On the other hand, the mechanism control unit 4 supplies a control signal to the couch / gantry mechanism unit 3 according to the instruction of the system control unit 11 to move the subject 30 with the top plate of the couch 1 at a constant speed in the body axis direction. While collecting projection data for the subject 30.

FIG. 15 shows the relationship between the slice position and TDC. FIG. 15A shows a photographed region of the head in the present embodiment. The first image is photographed at Z = Z1, and a scan for generating image data is performed at an interval ΔZ toward the top of the head. Is By this scanning, image reconstruction is performed for each projection data collected at the ΔZ interval to generate image data (step S55).

Next, a CT value γx at a preset ROI is measured for the image data obtained at each photographing position, and the measured value is stored in the CT value storage circuit 25 and displayed as TDC on the monitor 28 (step S56). ).

FIG. 15B shows the TDC displayed on the monitor 28. When the imaging slice is located in the brain of the subject 30, the CT value of normal brain tissue is obtained. However, with the movement of the imaging position, the CT value of the skull at Z = Z 1, and the CT value of air at Z = Z 2. The CT value is measured.

The CT value comparison circuit 29 in the CT value measurement unit 8 in FIG. 12 compares the CT value γx measured on the slice plane set at the ΔZ interval in the scanning direction with the threshold γ1. Then, when the CT value γx becomes equal to or greater than the threshold γ1, an imaging end instruction signal is supplied to the system control unit 11, and the system control unit 11 supplies a control signal to each unit to end the imaging.

In the above method, the display of the TDC is not necessarily required. In addition, the measured CT value or TDC is displayed on the display unit 9, and the operator determines the imaging end timing by observing the displayed CT value or TDC, and inputs an imaging end command from the input unit 10. May be. Also, a predetermined signal may be displayed on the display unit 9 or the input unit 10 when the CT value γx matches the threshold γ1.

Note that the CT value γx used for the above TDC display preferably uses the maximum value or the average value of the CT values obtained in, for example, a pixel unit in the set ROI.

On the other hand, in the above-described embodiment, the threshold γ1 is selected to detect the boundary between the brain tissue and the skull. However, the threshold γ2 may be selected to detect the boundary between the skull and the air.

(Modification)
Next, a modification of the fourth embodiment will be described with reference to FIGS. In this modification, instead of comparing the CT value γx with the threshold value γ1 or γ2 in the above-described fourth embodiment, the photographing end timing is set by comparing the number of pixels ηx having a CT value within a predetermined range with the threshold value η1. Perform

FIG. 16 is a block diagram showing the configuration of the X-ray CT apparatus according to the present modification. The difference from the first embodiment shown in FIG. It has been added to.

Then, the CT value calculation circuit 23 of the CT value measurement unit 8 measures the CT value γx in a pixel unit in a predetermined ROI of the image data obtained at a predetermined position, and stores the measurement result in the CT value storage circuit 25. I do. On the other hand, the pixel number comparison circuit 31 reads out the CT value γx in pixel units stored in the CT value storage circuit 25 and converts the CT value γx in a predetermined CT value range, that is, γa <γx <γb. The number ηx of the pixels having is counted. Further, the obtained number of pixels ηx is compared with a preset threshold η1 of the number of pixels.

Then, while moving the slice position in the scanning direction, the number of pixels ηx is compared with the threshold η1, and when ηx <η1, an instruction signal for terminating imaging is output.

Next, the shooting procedure of the present modification will be described with reference to the flowchart of FIG. However, in this flowchart, the same steps as those in the above-described fourth embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As in the first embodiment, the operator sets various conditions for imaging, the lower limit γa and the upper limit γb of the CT value range, and the threshold η1 of the number of pixels from the input unit 10. (Step S61). However, the lower limit value γa and the upper limit value γb of the CT value range are set by adding a margin to the maximum value and the minimum value of the CT value normally measured in the brain.

Next, the subject 30 is placed on the top of the couch 1, and the top plate and the subject 30 are placed on the body axis so that the diagnostic site (for example, the head) of the subject 30 is located at a predetermined position in the opening of the gantry. (Step S62). Then, first, preparation image data is photographed (step S63), and an ROI is set for this image data (step S64).

On the other hand, the mechanism control unit 4 supplies a control signal to the couch / gantry mechanism unit 3 and moves the subject 30 with the top board on the couch in the body axis direction at a constant speed, and outputs projection data to the subject 30. Collect.

FIG. 18 shows the relationship between the slice position and TDC. FIG. 18A shows a photographed region of the head in the present embodiment. The first image is photographed at Z = Z1, and a scan for generating image data is performed in the scan direction at an interval ΔZ. Is By this scanning, image data is generated by performing image reconstruction on each projection data obtained at the ΔZ interval (step S65).

Next, the CT value calculation circuit 23 measures the CT value γx in the ROI of the image data obtained at the predetermined position in pixel units (step S66), and stores the measurement result in the CT value storage circuit 25. On the other hand, the pixel number comparison circuit 31 compares the CT value γx of each pixel stored in the CT value storage circuit 25 with a predetermined CT value range, and determines a predetermined range, that is, γa <γx <γb. The number ηx of pixels having a CT value γx in the range is counted (step S67).

FIG. 18B shows a graph of the number of pixels ηx displayed on the monitor 28. When the ROI in the image data at the predetermined slice position is in the brain of the subject 30, most of the CT values γx are in the range of γa <γx <γb. On the other hand, when the ROI is set outside the brain, that is, in the skull or air, the CT value significantly deviates from the above range, so that the number of pixels ηx is equal to or smaller than the threshold η1.

The pixel number comparison circuit 29 in the CT value measurement unit 8 in FIG. 16 compares the pixel number ηx measured in a predetermined ROI of the slice plane set in the scanning direction at regular intervals with a preset threshold η1 (step S68). ). Then, when ηx <η1 is satisfied, an instruction signal for terminating photographing is supplied to the system control unit 11, and the system control unit 11 supplies a control signal to each unit and terminates photographing.

According to the above-described fourth embodiment and its modification, even in normal CT imaging, the apparatus provides the operator with the optimal timing for ending the imaging, or automatically sets the optimal timing. It is possible to minimize the amount of X-ray irradiation required.

The graph of the number of pixels shown in FIG. 18B may be displayed on the display unit 9, but this display is not always necessary. Alternatively, a graph of the number of pixels ηx may be displayed on the display unit 9, and the operator may determine a shooting end timing by observing the graph and input a shooting end command from the input unit 10. In this case, a predetermined signal may be displayed on the display unit 9 or the input unit 10 when the number of pixels ηx matches the threshold η1.

In the multi-slice method, for example, ROI based on the position information set in the preparation image is used for part or all of four pieces of image data obtained simultaneously at four slice positions having a slice thickness of 1 mm. May be set, but it is desirable to always set the ROI on the slice closest to the top of the head.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and may be modified and implemented. For example, although the scan method in the above-described embodiment has been described centering on the multi-slice method, the present invention is not limited to this.

Furthermore, although the method of determining the imaging end timing from the TDC has been described, the imaging end timing may be determined from a histogram obtained based on the CT values of a plurality of ROIs.

Further, in the above-described embodiment, when measuring the TDC, the first and second low X-ray image data or the high X-ray image data in which the ROI is displayed are displayed. The display of these image data does not have to be performed except when performing the above.

On the other hand, in the low X-ray scan, the method of increasing the scan interval to reduce the exposure dose compared to the high X-ray scan and the method of reducing the tube current have been described, but only one of them is performed. You may. Further, the operator may recognize an appropriate timing from the TDC characteristic of the high X-ray scan and input an imaging end instruction signal.

Furthermore, although the embodiment of the present invention has been described above using the third generation CT apparatus, the present invention is not limited to the third generation CT apparatus, and is applicable to other generation CT apparatuses such as the fourth generation. May be.

FIG. 1 is a block diagram illustrating a configuration of an X-ray CT apparatus according to a first embodiment of the present invention. FIG. 4 is a view showing an arrangement method of X-ray detection elements and “data bundling” in the embodiment. 5 is a flowchart showing a procedure for generating contrast dynamic CT image data in the embodiment. FIG. 4 is a diagram showing X-ray projection data acquisition conditions for low X-ray scan and high X-ray scan in the embodiment. FIG. 4 is a diagram showing a method of setting a CT value measurement ROI in the embodiment. FIG. 5 is a diagram showing TDC at the end of a first low X-ray scan in the embodiment. FIG. 4 is a diagram showing a TDC at the end of the high X-ray scan in the embodiment. 9 is a flowchart illustrating a procedure for generating contrast-enhanced dynamic CT image data according to the second embodiment of the present invention. FIG. 5 is a diagram showing TDC at the end of a first low X-ray scan in the embodiment. FIG. 9 is a diagram showing a modification of the CT image display in the first and second embodiments of the present invention. FIG. 7 is a diagram showing a modification of the TDC display in the embodiment. FIG. 9 is a block diagram illustrating a configuration of an X-ray CT apparatus according to a third embodiment of the present invention. 5 is a flowchart illustrating a procedure of capturing a contrast dynamic CT image according to the embodiment. 9 is a flowchart illustrating a procedure for capturing a CT image according to a fourth embodiment of the present invention. FIG. 4 is a diagram showing slice positions and TDC in the embodiment. FIG. 4 is a block diagram showing a configuration of an X-ray CT apparatus according to a modification of the embodiment. 9 is a flowchart showing a procedure for capturing a CT image in the modification. The figure which shows the slice position and the pixel number graph in the modification. The figure which shows the imaging method of the conventional contrast dynamic CT.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Couch 2 ... Cradle rotation part 3 ... Couch / cradle mechanism part 4 ... Mechanism control part 5 ... X-ray generation part 6 ... X-ray projection data collection part 7 ... Image generation part 8 ... CT value measurement part 9 ... Display part 10 ... Input unit 11 ... System control unit 12 ... High voltage generator 13 ... X-ray tube 14 ... X-ray aperture unit 15 ... Slip ring 16 ... X-ray detector 17 ... Switch group 18 ... DAS
19 Data transmission circuit 20 Projection data storage circuit 21 Reconstruction operation circuit 22 Image data storage circuit 23 CT value operation circuit 24 ROI position storage circuit 25 CT value storage circuit 26 Display storage circuit 27 Conversion Circuit 28 ... Monitor

Claims (22)

X-ray irradiation means for irradiating the subject with X-rays,
X-ray detection means for detecting X-rays transmitted through the subject,
Image data generating means for generating image data based on projection data at a desired position of the subject collected using the X-ray irradiating means and the X-ray detecting means,
A region-of-interest setting unit that sets a region of interest with respect to the first image data before the injection of the contrast agent obtained by the image data generating unit;
In parallel with the generation of a plurality of continuous second image data after the injection of the contrast agent by the image data generating means, the second image data based on the position information of the region of interest set by the region of interest setting means CT value measuring means for measuring a CT value in a region of interest set in the image data,
An X-ray CT apparatus comprising CT value display means for displaying a temporal change of a CT value measured by the CT value measurement means. Threshold setting means for setting a threshold related to a CT value;
CT value comparison means for comparing the threshold value and the CT value measured by the CT value measurement means with time,
2. The X-ray according to claim 1, wherein said CT value display means displays a timing signal at which a CT value measured by said CT value measurement means is substantially equal to a threshold value set by said threshold value setting means. CT device. 3. The X-ray according to claim 2, wherein the threshold value set by the threshold value setting unit is at least one of a CT value, a CT value change magnification, a CT value change curve slope, and a CT value change curve slope. CT device An irradiation condition setting unit configured to set an X-ray irradiation condition on the subject by the X-ray irradiation unit, wherein the irradiation condition setting unit changes the X-ray irradiation condition during a generation period of the second image data. 2. The X-ray CT apparatus according to claim 1, wherein X-ray irradiation means for irradiating the subject with X-rays,
X-ray detection means for detecting X-rays transmitted through the subject,
Image data generating means for generating image data based on projection data at a desired position of the subject collected using the X-ray irradiating means and the X-ray detecting means,
A region-of-interest setting unit that sets a region of interest with respect to the first image data before the injection of the contrast agent obtained by the image data generating unit;
In parallel with the generation of a plurality of continuous second image data after the injection of the contrast agent by the image data generating means, the second image data based on the position information of the region of interest set by the region of interest setting means CT value measuring means for measuring a CT value in a region of interest set in the image data,
Threshold setting means for setting a threshold related to a CT value;
CT value comparing means for comparing the CT value obtained by the CT value measuring means with the threshold value set by the threshold value setting means over time, and outputting a coincidence signal when the two substantially match each other;
An X-ray CT apparatus comprising: irradiation condition setting means for updating irradiation conditions for the subject based on an output signal of the CT value comparison means. The irradiation condition setting means sets a first irradiation condition for irradiating a low X-dose X-ray and a second irradiation condition for irradiating a high X-dose X-ray. The X-ray CT apparatus according to claim 5. In the generation of the second image data, the irradiation condition setting means may perform a first scan of the first irradiation condition, a second scan of the second irradiation condition, and a third scan of the first irradiation condition. The X-ray CT apparatus according to claim 6, wherein irradiation conditions for scanning are sequentially set. The irradiation condition setting means switches to the irradiation condition of the second scan when the CT value in the image data obtained by the first scan reaches a predetermined first threshold value. 8. The X-ray CT apparatus according to claim 7, wherein the irradiation condition for the third scan is switched when the CT value in the obtained image data reaches a predetermined second threshold value. The region-of-interest setting means identifies and sets a plurality of regions of interest in the first image data, respectively, and the CT value display means displays a CT value change curve obtained in the plurality of regions of interest in the region of interest. 2. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is displayed correspondingly. The X-ray CT apparatus according to claim 1, wherein the region of interest setting unit resets a region of interest using the second image data. The CT value measuring unit measures a plurality of CT values in pixel units in the region of interest of the image data set by the region of interest setting unit, and calculates either an average value or a maximum value of the measured CT values. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is a representative CT value. The said region-of-interest setting means adds a predetermined index which can be identified to at least one region of interest of a blood vessel region where a contrast agent arrives first and a blood vessel region which arrives latest. 6. The X-ray CT apparatus according to 5. The CT value display means separates a temporal change of a CT value in at least one of a blood vessel region where a contrast agent arrives first and a blood vessel region which arrives latest from a temporal change of a CT value in another region of interest. 2. The X-ray CT apparatus according to claim 1, wherein the image is displayed. 2. The X-ray CT according to claim 1, wherein the CT value display means displays a temporal change in a change with respect to a CT value of either the first image data or the initial second image data. apparatus. An image data storage unit, wherein the CT value measurement unit measures a CT value of a region of interest newly set by the region of interest setting unit with respect to the second image data stored by the image data storage unit 2. An X-ray CT apparatus according to claim 1, wherein said CT value display means displays a temporal change of a CT value in said region of interest retroactively. Image data display means, wherein the image data display means converts the second image data generated by the image data generation means and image data obtained by adding a boundary line of the region of interest to the second image data. The X-ray CT apparatus according to claim 1 or 5, wherein the X-ray CT apparatus is displayed separately. X-ray irradiation means for irradiating the subject with X-rays,
X-ray detection means for detecting X-rays transmitted through the subject,
Moving means for moving the subject in a predetermined direction,
Image data generation for generating a plurality of continuous image data based on projection data of the subject collected by using the X-ray irradiating means and the X-ray detecting means while moving the subject by the moving means Means,
A region of interest setting unit that sets a region of interest of a desired size for the image data generated by the image data generating unit;
An X-ray CT apparatus comprising: a CT value measuring unit that measures a CT value of the image data in the region of interest in parallel with the generation of the image data. Threshold value setting means for setting a threshold value for the CT value; comparing the CT value obtained by the CT value measuring means with the threshold value set by the threshold value setting means over time; 18. The X-ray CT apparatus according to claim 17, further comprising a CT value comparing unit that outputs an instruction signal for stopping the operation. X-ray irradiating means for irradiating X-rays in a plurality of directions of the subject,
X-ray detection means for detecting X-rays transmitted through the subject,
Moving means for moving the subject in a predetermined direction,
Image data generation for generating a plurality of continuous image data based on projection data of the subject collected by using the X-ray irradiating means and the X-ray detecting means while moving the subject by the moving means Means,
A region of interest setting unit that sets a region of interest of a desired size for the image data generated by the image data generating unit;
A CT value measuring unit that measures a CT value of the image data in the region of interest in pixel units, in parallel with the generation of the image data,
Range setting means for setting a range of CT values;
Pixel number calculation means for calculating the number of pixels in the region of interest, wherein the CT value measured by the CT value measurement means is included in the range set by the range setting means,
Threshold setting means for setting a threshold for the number of pixels;
The number of pixels obtained by the number-of-pixels calculation means is compared with the threshold value of the number of pixels set by the threshold value setting means with time, and an instruction signal for stopping X-ray irradiation is output when the two almost match. An X-ray CT apparatus, comprising: 20. The X-ray CT apparatus according to claim 19, further comprising a pixel number display unit, wherein the pixel number display unit displays a temporal change in the pixel number calculated by the pixel number calculation unit. Generating first image data before injection of a contrast agent at a desired position of the subject using the X-ray irradiation unit and the X-ray detection unit;
Setting a region of interest for measuring a CT value in the first image data;
Using the X-ray irradiating means and the X-ray detecting means, in parallel with the generation of a plurality of continuous second image data after the injection of the contrast agent performed at the desired position of the subject, the position of the region of interest Measuring a CT value in a region of interest set in the second image data based on information;
A CT value measuring method, comprising a step of displaying a temporal change of a CT value obtained by measurement. Setting a region of interest of a desired size at a desired position of the image data;
While moving the subject in a predetermined direction, in parallel with generation of a plurality of continuous second image data performed using the X-ray irradiating means and the X-ray detecting means, based on the position information of the region of interest, Measuring a CT value in a region of interest set in the second image data;
A CT value measuring method, comprising the step of terminating the X-ray irradiation unit of the X-ray irradiation unit based on the measured CT value.

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